This invention relates to rotary die cutting devices. More specifically, this invention relates to rotary die cutting apparatus for use to cut and/or score a web of material such as cardboard utilized in commercial boxes and the like.
The manufacture of many products such as cardboard boxes, paper products and the like involves the subjection of the raw material to a plurality of operating stations with the material being passed through the stations in continuous moving web form.
The manufacture of commercial cardboard cartons and similar products often involves passing a web of material through a gravure press consisting of a plurality of color stations. In this manner the web is provided with a multi-color print design and may also be provided with a varnish overcoating. Once the decorative functions have been completed the web material is passed through a die cutting machine so as to permit the application of desired die cuts and creases which are utilized in the assembly of the final product. A station may also be provided beyond the cutting station to strip out waste which may occur between the carton blanks and thereafter to deliver the blanks in shingled streams onto a delivery belt.
Two basic types of in-line die cutting apparatus have become known in the prior art. Conventional means to perform such in-line die cutting have comprised a reciprocating type platen which is designed to run in synchronization with the printing. Thus, between the last gravure station and the die cutting station there is provided an intermittent feeding station which permits momentary stopping of the web material so that the die platen may be closed to effect the desired cutting and creasing. Upon the completion of this operation the web is then accelerated to faster than the speed of operation of the web through the gravure stations so as to establish and maintain an average web velocity through all stations.
In addition to the fact that such reciprocating platen type die cutting apparatus require additional equipment for operation such as the accelerating devices previously referred to and devices such as accumulators which accommodate the acceleration, the reciprocal machines themselves have the disadvantage of being sensitive to misregistration as a result of the intermittent feeding. Further, the forces involved in acceleration limit the speed of the overall line because of the reciprocal dynamics experienced.
In order to avoid the problems of reciprocal misregistration, speed limitation and the requirement for additional capital expenditures, operational costs and maintenance attendant to the provision of auxillary equipment for use in operating reciprocal die cutting apparatus, the industry has resorted to the use of rotary die cutting apparatus.
A rotary die cutting apparatus eliminates the above stated problems because it comprises the utilization of a pair of rollers having grooves and lands formed on the surfaces thereof to form the desired cuts and scores. Further, by matching the surface rotational speed of the rollers to the desired speed of advance of the web through the remaining stations of the production line there is no necessity for intermittent operation, accumulators or other such auxillary equipment.
Because of the expense involved in producing rotary dies, such rotary die cutters in the past have been limited in their use to operations which involve extensive runs thus making relatively small the cost of the die cutting rollers per workpiece.
The advantages of rotary die cutting apparatus have been recognized and those skilled in these arts have attempted to reduce the cost per workpiece and thus broaden their utilization. Thus, typical dies for forming severence lines and methods for forming such severence lines are shown in three patents to Downie, U.S. Pat. No. 3,170,342, U.S. Pat. No. 3,244,335 and U.S. Pat. No. 3,142,233. Further, an advance in the manner of utilizing die sheets in conjunction with die rollers and in particular a structure for locking such die sheets in place to maintain a continuous die cutting surface as desired in the subject matter of my co-pending application, Ser. No. 860,691, filed Dec. 15, 1977, entitled ROTARY DIE LOCK STRUCTURE.
Although those skilled in the art have dealt with rotary die cutting apparatus and the problem of eliminating the necessity for intermittent advance of a web, two additional problems have been experienced. Initially, difficulties have occurred in maintaining running registration also known as rotary registration. Additionally, difficulties have been experienced in maintaining axis parallelism during operation.
For purposes of explanation, the term "running" or "rotary" registration means a registration as to the relative angular positions of the mating rollers of die cutting apparatus. Axis parallelism relates to the maintenance of a desired constant spacing between the surfaces of the rollers during operation so that proper relationship is established between the lands, cutting edges, rules and grooves utilized to form the desired cuts and grooves.
Various approaches have been taken with respect to establishing rotary registration. Thus, some apparatus permit adjustment of rotary registration by providing structure for effective disconnect of the roller from the roller drive mechanism so as to permit rotation of the roller independently therefrom. This approach, however, is disadvantageous because it requires termination of operation as well as at least partial disassembly of the apparatus in order to achieve the desired registration.
A second approach to achieving rotary registration has been through the use of plural gears. More specifically, through the use of a plurality of gears in the nature of planetary gearing, both the rotational reversal of direction as well as adjustment to rotating registry have been achievable. This approach, however, because of the plurality of gears involved, has been unsatisfactory where rotary registration is a critical factor in the production process. As will be recognized by those skilled in these arts, all gearing systems, by virtue of nothing more than acceptable tolerances, have a degree of play or "back lash". Such back lash causes an inherent registration problem. Thus, where a plurality of gears are utilized, the back lash problem may become cumulative thus causing such a degree of play as between the rollers of the die cutting apparatus that acceptable rotational or running registration becomes impossible. More specifically the degree of error introduced by what are otherwise acceptable tolerances creates a misregistration which is unacceptable and incapable of correction.
The second problem presented by known rotary cutting apparatus has been the ability to maintain axis parallelism, or, as it is sometimes known in the trade "impression" during operation. Axis parallelism at a particular desired spacing provides for the desired edge-to-edge, surface-to-surface or side-by-side relationship as among the lands, grooves, rules and other surfaces on the surface of the respective rotary die cutting rollers. In prior art structures, the operation of the apparatus and forces created thereby have tended to cause separation of the roller surfaces often at one end or the other depending upon where the highest cutting forces are generated, as a result of which the parallelism of the axes of the rollers is destroyed. With such parallelism destroyed the die rollers are no longer capable of adequately cutting or grooving and adjustment must be required.
An additional disadvantage of prior art structures has been that in order to change from one size die cutting roller to another in terms of roller circumference, prior art systems required the use of substitute circular pitch type and pitch line gearing. The substitution of the different gearing because of the change in circumference of the rollers is caused by the displacement of the axes of rotation. Needless to say the necessity of changing gearing when it is desired to change the size of rollers being accommodated greatly complicates the procedure and expense and is highly undesirable.